Li-Na Wu

Theoretical studies of the copper gyromagnetic factors for three novel Cu2+ coordination polymers with bi‐triazole ligand

The copper electron paramagnetic resonance gyromagnetic factors are theoretically studied for three novel Cu2+ coordination polymers [Cu(XL)(NO3)2]n (1), {[Cu(XL)(4,4′‐bpy)(NO3)2]•CH3CN}n (1a) and {[Cu(XL)3](NO3)2•3.5H2O}n (2) with bi‐triazole ligand (XL) = N,N′‐bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxdiimide bi(1,2,4‐triazole) from the high‐order perturbation calculations of the g factors for a rhombically elongated octahedral 3d9 group. The order (1 ≤ 1a < 2) of gz can be illustrated by the dominant second‐order perturbation term roughly proportional to the square of the covalency factor N. gx (and gy) relies on the combination of the contributions from N, cubic field parameter Dq, and axial elongation of the copper sites and exhibits the sequence (1 ≤ 2 < 1a). As regards the axiality (gx ≈ gy) of g factors, this is because the perpendicular rhombic contribution from the deviations of the bond lengths and bond angles for the planar ligands with respect to an ideal octahedron and that from the discrepancies between the crystal fields of the planar ligands O2− and N3− largely cancel each other. The present theoretical studies on the copper electron paramagnetic resonance g factors would be helpful to understand the structures and properties of some promising coordination polymers containing copper with the novel bi‐triazole ligand XL.

DFT calculations of the defect structures, electronic structures, and EPR parameters for three Rh2+ centers in AgCl

The local structures for various Rh2+ centers in AgCl are theoretically studied using density functional theory (DFT) with periodic CP2K program. Through geometry optimizing, the stable ground states with minimal energies and electronic structures are obtained for the tetragonally elongated (TE), orthorhombically elongated (OE), and tetragonally compressed (TC) centers, and the corresponding g and hyperfine coupling tensors are calculated in ORCA level. The calculations reveal obvious Jahn–Teller elongation distortions of about 0.109 and 0.110 Å along [001] axis for TE and OE centers without and with 1 next nearest neighbor (nnn) cation vacancy VAg in [100] axis, respectively. Whereas TC center with 1 nnn VAg along [001] axis exhibits moderate axial compression of about 0.066 Å due to the Jahn–Teller effect. For OE and TC centers with 1 nnn VAg, the ligand intervening in the central Rh2+ and the VAg is found to displace away from the VAg by about 0.028 and 0.024 Å, respectively. The present results are discussed and compared with those of the previous calculations based on the perturbation formulas by using the improved ligand field theory.

DFT Calculation of Rhodium-Doped Silver Bromide Crystals: Defect Structures, Photoelectric Property and EPR

Abstract AgBr crystals containing impurity Rh2+ with and without a next nearest neighbor silver vacancy (VAg) in the [001] axis are theoretically studied. The defect structures, bandgap, Mulliken charge, density of states, ultraviolet-visible (UV-Vis) and electron paramagnetic resonance spectra are analysed for two distinct (i.e. tetragonally elongated and compressed) centres by using density functional theory calculations. The results demonstrate that the structural, photoelectric and spectroscopic properties of AgBr are significantly changed after Rh substitution. The covalency of Rh-Br bonds in the two centres is stronger than that of pure AgBr according to the larger magnitudes of the overlap population. Compared to pure AgBr, Rh doping also results in significantly enhanced red shifts of absorption bands in the UV-Vis region and some new d-d transitions in the visible and near-infrared regions. Meanwhile, the bandgap of Rh-doped AgBr is about 10 % narrower than that of pure AgBr. As a result, the visible light activity may be enhanced in AgBr:Rh systems. Rh dopants can induce the magnetic moments of about 1.73 μB for both centres. Therefore, transition-metal Rh dopants may effectively modulate the electronic, optical and magnetic properties of AgBr.

Theoretical studies of the local structures and spin Hamiltonian parameters for Cu2+ in alkaline earth alumino borate glasses

The local structures and spin Hamiltonian parameters are theoretically studied for Cu2+ in alkaline earth alumino borate (XAB, X = Mg, Ca and Sr) glasses by using the perturbation calculations for tetragonally elongated octahedral 3d9 groups. The [CuO6]10− groups are subject to the large relative tetragonal elongation ratios of 15.4%, 13.4% and 13.0% for MgAB, CaAB and SrAB glasses, respectively, arising from the Jahn–Teller effect. The decreasing cubic field parameter Dq, orbital reduction factor k and relative elongation ratio with the increase of the radius of alkaline earth ion X from Mg to Ca or Sr are analyzed for the studied systems in a uniform way.

Theoretical studies of local structures and spin hamiltonian parameters for Cu2+ in alkali barium borate glasses

The local structures and spin Hamiltonian parameters are theoretically studied for Cu2+ in alkali barium borate glasses 20A2O ∙ 24.5BaO · 55B2O3 · 0.5CuO, where A = Li, Na and K by the quantitative calculations of these parameters for tetragonally elongated octahedral 3d9 clusters. The [CuO6]10‒ clusters are subject to the local relative tetragonal elongation ratios 7.8, 8.1 and 8.4% in Li, Na and K barium borate glasses, respectively, owing to the Jahn–Teller effect. The increasing (Li < Na < K) local relative elongation ratio and decreasing cubic field parameter and covalency factor are discussed in a consistent way.

Theoretical investigations of the EPR g factors and the local structures for Ni3+ in LiAlyCo1–yO2 at various Al concentrations

Abstract The electron paramagnetic resonance (EPR) g factors and local structures for Ni3+ in LiAlyCo1–yO2 as the cathode materials for lithium-ion batteries are theoretically investigated at various Al concentrations y (= 0.1, 0.5, 0.8 and 1.0). The [NiO6]9– clusters are subject to the tetragonal elongation distortions along the C4 axis owing to the Jahn–Teller effect and the different degrees of distortions are characterised by the slightly increasing relative elongation ratio ρ (and also crystal-field strength and covalency) with y. In pure LiAlO2 (y = 1.0), the [NiO6]9– cluster exhibits the largest ρ (≈1.4%) and an additional relative variation ratio τ (≈1.4%) of the planar bond lengths, responsible for the perpendicular g anisotropy δg = (gx – gy). The number of impurity Ni3+ centres increases from one at y = 0 and 1.0 to two at y = 0.1 and 0.8 and reaches the maximum four at y = 0.5, in accordance with the increasing degree of disorder of the systems. The distinct impurity centres for the same y may be accompanied by the comparable energies of the ground and near excited states, similar to ‘resonant states’ with slightly different local elongation distortions and tetragonal level splittings. The present studies will be helpful to understand the relationships between local structures and performances of LiAlyCo1–yO2 type cathode materials.